I have no personal experience to say how much damage you could cause by literally blowing on it (the danger of moisture from your breath condensing on the sensor) or from wiping with a cloth (the possibility ot scratching, or leaving behind smaller lint particles). Some say it's a very large danger, some say it's overstated. But do read up on the subject to at least know what the standard warnings are here. First line of defense should always be a simple rubber bulb (with intake filter) like the Rocket Blower; these and similar devices are widely available for just a few dollars at any camera store, Best Buy, etc.

After checking out the wealth of information that exists out there, i you still want to risk blowing and wiping, that's your business, but you do owe it to yourself to inform yourself at least a little.